Materials that exhibit UV-induced light transmission and electrical conductivity behavior.
Glasses that exhibit photochromic behavior have become well-known since their original introduction thirty-five years ago as phototropic glasses. Such glasses are activated, and caused to darken, by absorption of UV radiation.
Initially, photochromic glasses contained silver halide, other than fluoride, crystals as the UV responsive ingredient in an aluminosilicate base glass. Subsequently, glasses containing copper and/or cadmium halides, rather than silver, were discovered to be photochromic. Other materials, including a cadmium borosilicate glass family, have been described as exhibiting photochromic behavior. The commercial product has remained the silver halide-containing glass, however.
Transparent glass-ceramics having a metal fluoride crystal phase have recently been described as hosts for rare earth ions such as praseodymium (Pr+3). Such materials are used to produce opto-electronic devices, such as waveguide fibers, amplifiers and lasers. The present invention is predicated on discovery that the compositions of undoped, precursor glasses for these glass-ceramics can be modified to produce glasses exhibiting unusual behavior. In particular, glasses having such modified compositions exhibit UV-induced changes in light transmission and electrical conductivity. This unusual behavior is also observed in the glass-ceramic state.
It is a purpose of the invention to provide a unique material that exhibits these unusual effects in the glassy state, as well as in the glass-ceramic state.
It is a further purpose to provide articles that exhibit these UV-induced changes.
A still further purpose is to provide a method of producing such unique articles.
Prior literature of possible interest is supplied separately.